This invention relates to an isostatic press mold for producing moldings from ceramic material.
In German Patent Specification No. 3,101,236 there is disclosed an isostatic press mold comprising two mold parts which are movable relative to one another between a mold-closed position and a mold-open position and which, in the mold-closed position, define between them a mold cavity, there being, on at least one of the mold parts, a press diagraphm which on one side defines part of the limiting surfaces of the mold cavity and on the other side can be subjected to a pressure fluid, especially a pressure liquid.
In the known embodiment, the press diaphragm is relatively thin-walled. This thin-walled press diaphragm has hitherto been considered necessary because internal stresses in the elastomeric material of the press diaphragm can be kept within acceptable limits in this way. Excessive internal shearing stresses and compressive stresses in the press diaphragm must be avoided if the deformation behaviour of the press diaphragm during the pressing operation is to be controlled at all.
On the other hand, if the press diaphragm has a small wall thickness it is easy for the contours of the molding material which is being pressed by the press diaphragm to become blurred, because the press diaphragm, which is supported by an hydraulic pressure medium, behaves in a similar way to a "waterbed", that is to say it can be deformed in an indeterminable way.
The object of the present invention is therefore to provide an isostatic press mold such that, whilst excessive internal stresses within the press diaphragm are avoided, it is possible to produce clearly defined contours in the molding material by means of the surface of the press diaphragm facing the mold cavity.